package com.javaxiaobear.base.common.utils.html;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * HTML过滤器，用于去除XSS漏洞隐患。
 *
 * @author javaxiaobear
 */
public final class HTMLFilter {
  /** regex flag union representing /si modifiers in php */
  private static final int REGEX_FLAGS_SI = Pattern.CASE_INSENSITIVE | Pattern.DOTALL;

  private static final Pattern P_COMMENTS = Pattern.compile("<!--(.*?)-->", Pattern.DOTALL);
  private static final Pattern P_COMMENT = Pattern.compile("^!--(.*)--$", REGEX_FLAGS_SI);
  private static final Pattern P_TAGS = Pattern.compile("<(.*?)>", Pattern.DOTALL);
  private static final Pattern P_END_TAG = Pattern.compile("^/([a-z0-9]+)", REGEX_FLAGS_SI);
  private static final Pattern P_START_TAG =
      Pattern.compile("^([a-z0-9]+)(.*?)(/?)$", REGEX_FLAGS_SI);
  private static final Pattern P_QUOTED_ATTRIBUTES =
      Pattern.compile("([a-z0-9]+)=([\"'])(.*?)\\2", REGEX_FLAGS_SI);
  private static final Pattern P_UNQUOTED_ATTRIBUTES =
      Pattern.compile("([a-z0-9]+)(=)([^\"\\s']+)", REGEX_FLAGS_SI);
  private static final Pattern P_PROTOCOL = Pattern.compile("^([^:]+):", REGEX_FLAGS_SI);
  private static final Pattern P_ENTITY = Pattern.compile("&#(\\d+);?");
  private static final Pattern P_ENTITY_UNICODE = Pattern.compile("&#x([0-9a-f]+);?");
  private static final Pattern P_ENCODE = Pattern.compile("%([0-9a-f]{2});?");
  private static final Pattern P_VALID_ENTITIES = Pattern.compile("&([^&;]*)(?=(;|&|$))");
  private static final Pattern P_VALID_QUOTES =
      Pattern.compile("(>|^)([^<]+?)(<|$)", Pattern.DOTALL);
  private static final Pattern P_END_ARROW = Pattern.compile("^>");
  private static final Pattern P_BODY_TO_END = Pattern.compile("<([^>]*?)(?=<|$)");
  private static final Pattern P_XML_CONTENT = Pattern.compile("(^|>)([^<]*?)(?=>)");
  private static final Pattern P_STRAY_LEFT_ARROW = Pattern.compile("<([^>]*?)(?=<|$)");
  private static final Pattern P_STRAY_RIGHT_ARROW = Pattern.compile("(^|>)([^<]*?)(?=>)");
  private static final Pattern P_AMP = Pattern.compile("&");
  private static final Pattern P_QUOTE = Pattern.compile("\"");
  private static final Pattern P_LEFT_ARROW = Pattern.compile("<");
  private static final Pattern P_RIGHT_ARROW = Pattern.compile(">");
  private static final Pattern P_BOTH_ARROWS = Pattern.compile("<>");

  // @xxx could grow large... maybe use sesat's ReferenceMap
  private static final ConcurrentMap<String, Pattern> P_REMOVE_PAIR_BLANKS =
      new ConcurrentHashMap<>();
  private static final ConcurrentMap<String, Pattern> P_REMOVE_SELF_BLANKS =
      new ConcurrentHashMap<>();

  /** set of allowed html elements, along with allowed attributes for each element */
  private final Map<String, List<String>> vAllowed;

  /** counts of open tags for each (allowable) html element */
  private final Map<String, Integer> vTagCounts = new HashMap<>();

  /** html elements which must always be self-closing (e.g. "<img />") */
  private final String[] vSelfClosingTags;

  /** html elements which must always have separate opening and closing tags (e.g. "<b></b>") */
  private final String[] vNeedClosingTags;

  /** set of disallowed html elements */
  private final String[] vDisallowed;

  /** attributes which should be checked for valid protocols */
  private final String[] vProtocolAtts;

  /** allowed protocols */
  private final String[] vAllowedProtocols;

  /** tags which should be removed if they contain no content (e.g. "<b></b>" or "<b />") */
  private final String[] vRemoveBlanks;

  /** entities allowed within html markup */
  private final String[] vAllowedEntities;

  /** flag determining whether comments are allowed in input String. */
  private final boolean stripComment;

  private final boolean encodeQuotes;

  /**
   * flag determining whether to try to make tags when presented with "unbalanced" angle brackets
   * (e.g. "<b text </b>" becomes "<b> text </b>"). If set to false, unbalanced angle brackets will
   * be html escaped.
   */
  private final boolean alwaysMakeTags;

  /** Default constructor. */
  public HTMLFilter() {
    vAllowed = new HashMap<>();

    final ArrayList<String> a_atts = new ArrayList<>();
    a_atts.add("href");
    a_atts.add("target");
    vAllowed.put("a", a_atts);

    final ArrayList<String> img_atts = new ArrayList<>();
    img_atts.add("src");
    img_atts.add("width");
    img_atts.add("height");
    img_atts.add("alt");
    vAllowed.put("img", img_atts);

    final ArrayList<String> no_atts = new ArrayList<>();
    vAllowed.put("b", no_atts);
    vAllowed.put("strong", no_atts);
    vAllowed.put("i", no_atts);
    vAllowed.put("em", no_atts);

    vSelfClosingTags = new String[] {"img"};
    vNeedClosingTags = new String[] {"a", "b", "strong", "i", "em"};
    vDisallowed = new String[] {};
    vAllowedProtocols = new String[] {"http", "mailto", "https"}; // no ftp.
    vProtocolAtts = new String[] {"src", "href"};
    vRemoveBlanks = new String[] {"a", "b", "strong", "i", "em"};
    vAllowedEntities = new String[] {"amp", "gt", "lt", "quot"};
    stripComment = true;
    encodeQuotes = true;
    alwaysMakeTags = false;
  }

  /**
   * Map-parameter configurable constructor.
   *
   * @param conf map containing configuration. keys match field names.
   */
  @SuppressWarnings("unchecked")
  public HTMLFilter(final Map<String, Object> conf) {

    assert conf.containsKey("vAllowed") : "configuration requires vAllowed";
    assert conf.containsKey("vSelfClosingTags") : "configuration requires vSelfClosingTags";
    assert conf.containsKey("vNeedClosingTags") : "configuration requires vNeedClosingTags";
    assert conf.containsKey("vDisallowed") : "configuration requires vDisallowed";
    assert conf.containsKey("vAllowedProtocols") : "configuration requires vAllowedProtocols";
    assert conf.containsKey("vProtocolAtts") : "configuration requires vProtocolAtts";
    assert conf.containsKey("vRemoveBlanks") : "configuration requires vRemoveBlanks";
    assert conf.containsKey("vAllowedEntities") : "configuration requires vAllowedEntities";

    vAllowed = Collections.unmodifiableMap((HashMap<String, List<String>>) conf.get("vAllowed"));
    vSelfClosingTags = (String[]) conf.get("vSelfClosingTags");
    vNeedClosingTags = (String[]) conf.get("vNeedClosingTags");
    vDisallowed = (String[]) conf.get("vDisallowed");
    vAllowedProtocols = (String[]) conf.get("vAllowedProtocols");
    vProtocolAtts = (String[]) conf.get("vProtocolAtts");
    vRemoveBlanks = (String[]) conf.get("vRemoveBlanks");
    vAllowedEntities = (String[]) conf.get("vAllowedEntities");
    stripComment = conf.containsKey("stripComment") ? (Boolean) conf.get("stripComment") : true;
    encodeQuotes = conf.containsKey("encodeQuotes") ? (Boolean) conf.get("encodeQuotes") : true;
    alwaysMakeTags =
        conf.containsKey("alwaysMakeTags") ? (Boolean) conf.get("alwaysMakeTags") : true;
  }

  private void reset() {
    vTagCounts.clear();
  }

  // ---------------------------------------------------------------
  // my versions of some PHP library functions
  public static String chr(final int decimal) {
    return String.valueOf((char) decimal);
  }

  public static String htmlSpecialChars(final String s) {
    String result = s;
    result = regexReplace(P_AMP, "&amp;", result);
    result = regexReplace(P_QUOTE, "&quot;", result);
    result = regexReplace(P_LEFT_ARROW, "&lt;", result);
    result = regexReplace(P_RIGHT_ARROW, "&gt;", result);
    return result;
  }

  // ---------------------------------------------------------------

  /**
   * given a user submitted input String, filter out any invalid or restricted html.
   *
   * @param input text (i.e. submitted by a user) than may contain html
   * @return "clean" version of input, with only valid, whitelisted html elements allowed
   */
  public String filter(final String input) {
    reset();
    String s = input;

    s = escapeComments(s);

    s = balanceHTML(s);

    s = checkTags(s);

    s = processRemoveBlanks(s);

    // s = validateEntities(s);

    return s;
  }

  public boolean isAlwaysMakeTags() {
    return alwaysMakeTags;
  }

  public boolean isStripComments() {
    return stripComment;
  }

  private String escapeComments(final String s) {
    final Matcher m = P_COMMENTS.matcher(s);
    final StringBuffer buf = new StringBuffer();
    if (m.find()) {
      final String match = m.group(1); // (.*?)
      m.appendReplacement(buf, Matcher.quoteReplacement("<!--" + htmlSpecialChars(match) + "-->"));
    }
    m.appendTail(buf);

    return buf.toString();
  }

  private String balanceHTML(String s) {
    if (alwaysMakeTags) {
      //
      // try and form html
      //
      s = regexReplace(P_END_ARROW, "", s);
      // 不追加结束标签
      s = regexReplace(P_BODY_TO_END, "<$1>", s);
      s = regexReplace(P_XML_CONTENT, "$1<$2", s);

    } else {
      //
      // escape stray brackets
      //
      s = regexReplace(P_STRAY_LEFT_ARROW, "&lt;$1", s);
      s = regexReplace(P_STRAY_RIGHT_ARROW, "$1$2&gt;<", s);

      //
      // the last regexp causes '<>' entities to appear
      // (we need to do a lookahead assertion so that the last bracket can
      // be used in the next pass of the regexp)
      //
      s = regexReplace(P_BOTH_ARROWS, "", s);
    }

    return s;
  }

  private String checkTags(String s) {
    Matcher m = P_TAGS.matcher(s);

    final StringBuffer buf = new StringBuffer();
    while (m.find()) {
      String replaceStr = m.group(1);
      replaceStr = processTag(replaceStr);
      m.appendReplacement(buf, Matcher.quoteReplacement(replaceStr));
    }
    m.appendTail(buf);

    // these get tallied in processTag
    // (remember to reset before subsequent calls to filter method)
    final StringBuilder sBuilder = new StringBuilder(buf.toString());
    for (String key : vTagCounts.keySet()) {
      for (int ii = 0; ii < vTagCounts.get(key); ii++) {
        sBuilder.append("</").append(key).append(">");
      }
    }
    s = sBuilder.toString();

    return s;
  }

  private String processRemoveBlanks(final String s) {
    String result = s;
    for (String tag : vRemoveBlanks) {
      if (!P_REMOVE_PAIR_BLANKS.containsKey(tag)) {
        P_REMOVE_PAIR_BLANKS.putIfAbsent(
            tag, Pattern.compile("<" + tag + "(\\s[^>]*)?></" + tag + ">"));
      }
      result = regexReplace(P_REMOVE_PAIR_BLANKS.get(tag), "", result);
      if (!P_REMOVE_SELF_BLANKS.containsKey(tag)) {
        P_REMOVE_SELF_BLANKS.putIfAbsent(tag, Pattern.compile("<" + tag + "(\\s[^>]*)?/>"));
      }
      result = regexReplace(P_REMOVE_SELF_BLANKS.get(tag), "", result);
    }

    return result;
  }

  private static String regexReplace(
      final Pattern regex_pattern, final String replacement, final String s) {
    Matcher m = regex_pattern.matcher(s);
    return m.replaceAll(replacement);
  }

  private String processTag(final String s) {
    // ending tags
    Matcher m = P_END_TAG.matcher(s);
    if (m.find()) {
      final String name = m.group(1).toLowerCase();
      if (allowed(name)) {
        if (!inArray(name, vSelfClosingTags)) {
          if (vTagCounts.containsKey(name)) {
            vTagCounts.put(name, vTagCounts.get(name) - 1);
            return "</" + name + ">";
          }
        }
      }
    }

    // starting tags
    m = P_START_TAG.matcher(s);
    if (m.find()) {
      final String name = m.group(1).toLowerCase();
      final String body = m.group(2);
      String ending = m.group(3);

      // debug( "in a starting tag, name='" + name + "'; body='" + body + "'; ending='" + ending +
      // "'" );
      if (allowed(name)) {
        final StringBuilder params = new StringBuilder();

        final Matcher m2 = P_QUOTED_ATTRIBUTES.matcher(body);
        final Matcher m3 = P_UNQUOTED_ATTRIBUTES.matcher(body);
        final List<String> paramNames = new ArrayList<>();
        final List<String> paramValues = new ArrayList<>();
        while (m2.find()) {
          paramNames.add(m2.group(1)); // ([a-z0-9]+)
          paramValues.add(m2.group(3)); // (.*?)
        }
        while (m3.find()) {
          paramNames.add(m3.group(1)); // ([a-z0-9]+)
          paramValues.add(m3.group(3)); // ([^\"\\s']+)
        }

        String paramName, paramValue;
        for (int ii = 0; ii < paramNames.size(); ii++) {
          paramName = paramNames.get(ii).toLowerCase();
          paramValue = paramValues.get(ii);

          // debug( "paramName='" + paramName + "'" );
          // debug( "paramValue='" + paramValue + "'" );
          // debug( "allowed? " + vAllowed.get( name ).contains( paramName ) );

          if (allowedAttribute(name, paramName)) {
            if (inArray(paramName, vProtocolAtts)) {
              paramValue = processParamProtocol(paramValue);
            }
            params.append(' ').append(paramName).append("=\\\"").append(paramValue).append("\\\"");
          }
        }

        if (inArray(name, vSelfClosingTags)) {
          ending = " /";
        }

        if (inArray(name, vNeedClosingTags)) {
          ending = "";
        }

        if (ending == null || ending.length() < 1) {
          if (vTagCounts.containsKey(name)) {
            vTagCounts.put(name, vTagCounts.get(name) + 1);
          } else {
            vTagCounts.put(name, 1);
          }
        } else {
          ending = " /";
        }
        return "<" + name + params + ending + ">";
      } else {
        return "";
      }
    }

    // comments
    m = P_COMMENT.matcher(s);
    if (!stripComment && m.find()) {
      return "<" + m.group() + ">";
    }

    return "";
  }

  private String processParamProtocol(String s) {
    s = decodeEntities(s);
    final Matcher m = P_PROTOCOL.matcher(s);
    if (m.find()) {
      final String protocol = m.group(1);
      if (!inArray(protocol, vAllowedProtocols)) {
        // bad protocol, turn into local anchor link instead
        s = "#" + s.substring(protocol.length() + 1);
        if (s.startsWith("#//")) {
          s = "#" + s.substring(3);
        }
      }
    }

    return s;
  }

  private String decodeEntities(String s) {
    StringBuffer buf = new StringBuffer();

    Matcher m = P_ENTITY.matcher(s);
    while (m.find()) {
      final String match = m.group(1);
      final int decimal = Integer.decode(match).intValue();
      m.appendReplacement(buf, Matcher.quoteReplacement(chr(decimal)));
    }
    m.appendTail(buf);
    s = buf.toString();

    buf = new StringBuffer();
    m = P_ENTITY_UNICODE.matcher(s);
    while (m.find()) {
      final String match = m.group(1);
      final int decimal = Integer.valueOf(match, 16).intValue();
      m.appendReplacement(buf, Matcher.quoteReplacement(chr(decimal)));
    }
    m.appendTail(buf);
    s = buf.toString();

    buf = new StringBuffer();
    m = P_ENCODE.matcher(s);
    while (m.find()) {
      final String match = m.group(1);
      final int decimal = Integer.valueOf(match, 16).intValue();
      m.appendReplacement(buf, Matcher.quoteReplacement(chr(decimal)));
    }
    m.appendTail(buf);
    s = buf.toString();

    s = validateEntities(s);
    return s;
  }

  private String validateEntities(final String s) {
    StringBuffer buf = new StringBuffer();

    // validate entities throughout the string
    Matcher m = P_VALID_ENTITIES.matcher(s);
    while (m.find()) {
      final String one = m.group(1); // ([^&;]*)
      final String two = m.group(2); // (?=(;|&|$))
      m.appendReplacement(buf, Matcher.quoteReplacement(checkEntity(one, two)));
    }
    m.appendTail(buf);

    return encodeQuotes(buf.toString());
  }

  private String encodeQuotes(final String s) {
    if (encodeQuotes) {
      StringBuffer buf = new StringBuffer();
      Matcher m = P_VALID_QUOTES.matcher(s);
      while (m.find()) {
        final String one = m.group(1); // (>|^)
        final String two = m.group(2); // ([^<]+?)
        final String three = m.group(3); // (<|$)
        // 不替换双引号为&quot;，防止json格式无效 regexReplace(P_QUOTE, "&quot;", two)
        m.appendReplacement(buf, Matcher.quoteReplacement(one + two + three));
      }
      m.appendTail(buf);
      return buf.toString();
    } else {
      return s;
    }
  }

  private String checkEntity(final String preamble, final String term) {

    return ";".equals(term) && isValidEntity(preamble) ? '&' + preamble : "&amp;" + preamble;
  }

  private boolean isValidEntity(final String entity) {
    return inArray(entity, vAllowedEntities);
  }

  private static boolean inArray(final String s, final String[] array) {
    for (String item : array) {
      if (item != null && item.equals(s)) {
        return true;
      }
    }
    return false;
  }

  private boolean allowed(final String name) {
    return (vAllowed.isEmpty() || vAllowed.containsKey(name)) && !inArray(name, vDisallowed);
  }

  private boolean allowedAttribute(final String name, final String paramName) {
    return allowed(name) && (vAllowed.isEmpty() || vAllowed.get(name).contains(paramName));
  }
}
